THE FIRES WITHIN
'This,' said Karn smugly, 'will interest you. Just
take a look at it!'
He pushed across the file he had been reading, and
for the nth time I decided to ask for his transfer or,
failing that, my own.
'What's it about?' I said wearily.
'It's a long report from a Dr. Matthews to the Minister 
of Science.' He waved it in front of me. 'Just read
it!'
Without much enthusiasm, I began to go through
the file. A few minutes later I looked up and admitted
grudgingly: 'Maybe you're right - this time.' I didn' t
speak again until I'd finished....

My dear Minister (the letter began). As you requested, 
here is my special report on Professor Hancock's 
experiments, which have had such unexpected
and extraordinary results. I have not had time to cast it
into a more orthodox form, but am sending you the
dictation just as it stands.
Since you have many matters engaging your attention, 
perhaps I should briefly summarize our dealings
with Professor Hancock. Until 1955, the Professor held
the Kelvin Chair of Electrical Engineering at Brendon
University, from which he was granted indefinite leave
of absense to carry out his researches. In these he was
joined by the late Dr. Clayton, sometime Chief Geologist 
to the Ministry of Fuel and Power. Their joint
research was financed by grants from the Paul Fund
and the Royal Society.
The Professor hoped to develop sonar as a means of
precise geological surveying sonar, as you will know,
is the acoustic equivalent of radar, and although less
familiar is older by some millions of years, since bats
use it very effectively to detect insects and obstacles at
night. Professor Haneock intended to send highpowered 
supersonic pulses into the ground and to
build up from the returning echoes an image of what
lay beneath. The picture would be displayed on a
cathode ray tube and the whole system would be
exactly analogous to the type of radar used in aircraft
to show the ground through cloud.
In 1957 the two scientists had achieved partial success 
but had exhausted their funds. Early in 1958 they
applied directly to the government for a block grant.
Dr. Clayton pointed out the immense value of a device 
which would enable us to take a kind of X-ray
photo of the Earth's crust, and the Minister of Fuel
gave it his approval before passing on the application
to us. At that time the report of the Bernal Committee
had just been published and we were very anxious that
deserving cases should be dealt with quickly to avoid
further criticisms. I went to see the Professor at once
and submitted a favorable report; the first payment of
our grant (5/513A/68) was made a few days later.
From that time I have been continually in touch with
the research and have assisted to some extent with
technical advice.
The equipment used in the experiments is complex,
but its principles are simple. Very short but extremely
powerful pulses of supersonic waves are generated by a
special transmitter which revolves continuously in a
pool of a heavy organic liquid, The beam produced
passes into the ground and 'scans' like a radar beam
searching for echoes. By a very ingenious time-delay
circuit which I will resist the temptation to describe,
echoes from any depth can be selected and so pictures
of the strata under investigation can be built up on a
cathode ray screen in the normal way.
When I first met Professor Hancock his apparatus
was rather primitive, but he was able to show me the
distribution of rock down to a depth of several hundred 
feet and we could see quite elearly a part of the
Bakerloo Line which passed very near his laboratory.
Much of the Professor's success was due to the great
intensity of his supersonic bursts; almost from the beginning 
he was able to generate peak powers of several
hundred kilowatts, nearly all of which was radiated
into the ground. It was unsafe to remain near the
transmitter, and I noticed that the soil became quite
warm around it. I was rather surprised to see large
numbers of birds in the vicinity, but soon discovered
that they were attracted by the hundreds of dead
worms lying on the ground.
At the time of Dr. Clayton's death in 1960, the
equipment was working at a power level of over a
megawatt and quite good pictures of strata a mile down
could be obtained. Dr. Clayton had correlated the results 
with known geographical surveys, and had
proved beyond doubt the value of the information
obtained.
Dr. Clavton' s death in a motor accident was a great
tragedy. He had always exerted a stabilizing influence
on the Professor, who had never been much interested
in the practical applications of his work. Soon afterward 
I noticed a distinct change in the Professor's outlook, 
and a few months later he confided his new
ambitions to me. I had been trying to persuade him to
publish his results (he had already spent over £50.000
and the Public Accounts Committee was being difficult 
again), but he asked for a little more time. I think
I can best explain his attitude by his own words, which
I remember very vividly, for they were expressed with
peculiar emphasis.
'Have you ever wondered,' he said, 'what the Earth
really is like inside? We've only scratched the surface
with our mines and wells. What lies beneath is as unknown 
as the other side of the Moon.
'We know that the Earth is unnaturally dense - far
denser than the rocks and soil of its crust would indicate. 
The core may be solid metal, but until now 
there's been no way of telling. Even ten miles down 
the pressure must be thirty tons or more to the square 
inch and the temperature several hundred degrees. 
What it's like at the center staggers the imagination: 
the pressure must be thousands of tons to the square 
inch. It's strange to think that in two or three years we 
may have reached the Moon, but when we've got to 
the stars we'll still be no nearer that inferno four 
thousand miles beneath our feet.
'I can now get recognizable echoes from two miles 
down, but I hope to step up the transmitter to ten 
megawatts in a few months. With that power, I believe 
the range will be increased to ten miles; and I don't 
mean to stop there.'
I was impressed, but at the same time I felt a little 
skeptical.
'That's all very well,' I said, 'but surely the deeper 
you go the less there'll be to see. The pressure will 
make any cavities impossible, and after a few miles 
there will simply be a homogeneous mass getting denser 
and denser.'
Quite likely,' agreed the Professor. 'But I can still 
learn a lot from the transmission characteristics. Anyway 
we'll see when we get there!'
That was four months ago; and yesterday I saw the 
result of that research. When I answered his invitation 
the Professor was clearly excited, but he gave me no 
hint of what, if anything, he had discovered. He 
showed me his improved equipment and raised the 
new receiver from its bath. The sensitivity of the pickups 
had been greatly improved and this alone had 
effectively doubled the range, altogether apart from 
the increased transmitter power. It was strange to 
watch the steel framework slowly turning and to 
realize that it was exploring regions, which, in spite of 
their nearness, man might never reach.
When we entered the hut containing the display
equipment, the Professor was strangely silent. He 
switched on the transmitter, and even though it was a 
hundred yards away I could feel an uncomfortable 
tingling. Then the cathode ray tube lit up and the 
slowly revolving timebase drew the picture I had seen 
so often before. Now, however, the definition was 
much improved owing to the increased power and sensitivity 
of the equipment. I adjusted the depth control 
and focused on the Underground, which was dearly 
visible as a dark line across the faintly luminous 
screen. While I was watching, it suddenly seemed to 
fill with mist and I knew that a train was going 
through.
Presently I continued the descent. Although I had 
watched this picture many times before it was always 
uncanny to see great luminous masses floating toward 
me and to know that they were buried rocks - perhaps 
the debris from the glaciers of fifty thousand years ago. 
Dr. Clayton had worked out a chart so that we could 
identify the various strata as they were passed, and 
presently I saw that I was through the alluvial soil and 
entering the great clay saucer which traps and holds 
the city's artesian water. Soon that too was passed, and 
I was dropping down through the bedrock almost a 
mile below the surface.
The picture was still clear and bright, though there 
was little to see, for there were now few changes in the 
ground structure. The pressure was already rising to 
a thousand atmospheres; soon it would be impossible 
for any cavity to remain open, for the rock itself would 
begin to flow. Mile after mile I sank, but only a pale 
mist floated on the screen, broken sometimes when 
echoes were returned from pockets or lodes of denser 
material. They became fewer and fewer as the depth 
increased - or else they were now so small that they 
could no longer be seen.
The scale of the picture was, of course, continually 
expanding. It was now many miles from side to side, 
and I felt like an airman looking down upon an unbroken 
cloud ceiling from an enormous height. For a 
moment a sense of vertigo seized me as I thought of 
the abyss into which I was gazing. I do not think that 
the world will ever seem quite solid to me again.
At a depth of nearly ten miles I stopped and looked 
at the Professor. There had been no alteration for some 
time, and I knew that the rock must now be compressed 
into a featureless, homogeneous mass. I did a 
quick mental calculation and shuddered as I realized 
that the pressure must be at least thirty tons to the 
square inch. The scanner was revolving very slowly 
now, for the feeble echoes were taking many seconds 
to struggle back from the depths.
'Well, Professor,' I said, I congratulate you. It's a 
wonderful achievement. But we seem to have reached 
the core now. I don't suppose there'll be any change 
from here to the center.'
He smiled a little wryly. 'Go on,' he said. 'You 
haven't finished yet.'
There was something in his voice that puzzled and 
alarmed me. I looked at him intently for a moment; 
his features were just visible in the blue-green glow 
of the cathode ray tube.
'How far down can this thing go?' I asked, as the 
interminable descent started again.
'Fifteen miles,' he said shortly. I wondered how he 
knew, for the last feature I had seen at all clearly 
was only eight miles down. But I continued the long 
fall through the rock, the scanner turning more and 
more slowly now, until it took almost five minutes 
to make a complete revolution. Behind me I could 
hear the Professor breathing heavily, and once the 
back of my chair gave a crack as his fingers gripped 
it.
Then, suddenly, very faint markings began to reappear 
on the screen. I leaned forward eagerly, wondering 
if this was the first glimpse of the world's 
iron core. With agonizing slowness the scanner turned 
through a right angle, then another. And then - 
I leaped suddenly out of my chair, cried 'My God!' 
and turned to face the Professor. Only once before in 
my life had I received such an intellectual shock - fifteen 
years ago, when I had accidentally turned on 
the radio and heard of the fall of the first atomic bomb. 
That had been unexpected, but this was inconceivable. 
For on the screen had appeared a grid of faint 
lines crossing and recrossing to form a perfectly symmetrical 
lattice.
I know that I said nothing for many minutes, for 
the scanner made a complete revolution while I stood 
frozen with surprise. Then the Professor spoke in a 
soft, unnaturally calm voice.
`I wanted you to see it for yourself before I said anything. 
That picture is now thirty miles in diameter, 
and those squares are two or three miles on a side. 
You'll notice that the vertical lines converge and the 
horizontal ones are bent into arcs. We're looking at 
part of an enormous structure of concentric rings the 
center must lie many miles to the north, probably in 
the region of Cambridge. How much further it extends 
in the other direction we can only guess.'
'But what is it, for heaven's sake?' 
'Well, it's clearly artificial.´ 
'That's ridiculous! Fifteen miles down!'
The Professor pointed to the screen again. 'God 
knows I've done my best,' he said, 'but I can't convince 
myself that Nature could make anything like that.'
I had nothing to say, and presently he continued: 'I 
discovered it three days ago, when I a as trying to find 
the maximum range of the equipment I can go deeper 
than this. and I rather think that the structure we can 
see is so dense that it won't transmit my radiations any 
further.
I've tried a dozen theories, but in the end I keep 
returning to one. We know that the pressure down 
there must be eight or nine thousand atmospheres, and 
the temperature must be high enough to melt rock. 
But normal matter is still almost empty space. Suppose
that there is life down there - not organic life, of 
course, but life based on partially condensed matter, 
matter in which the electron shells are few or altogether 
missing. Do you see what I mean? To such 
creatures, even the rock fifteen miles down would offer 
no more resistance than water - and we and all our 
world would be as tenuous as ghosts.'
'Then that thing we can see - ´
'Is a city, or its equivalent. You've seen its size, so 
you can judge for yourself the civilization that must 
have built it. All the world we know - our oceans and 
continents and mountains-is nothing more than a 
film of mist surrounding something beyond our comprehension:
Neither of us said anything for a while I remember 
feeling a foolish surprise at being one of the first men 
in the world to learn the appalling truth; for somehow 
I never doubted that it was the truth. And I 
wondered how the rest of humanity would react when 
the revelation came.
Presently I broke into the silence. 'If you're right,´ 
I said, 'why have they - whatever they are - never 
made contact with us?'
The Professor looked at me rather pityingly. 'We 
think we're good engineers,' he said, 'but how could 
we reach them? Besides, I'm not at all sure that there 
haven't been contacts. Think of all the underground 
creatures and the mythology - trolls and cobalds and 
the rest. No, it's quite impossible - I take it back. Still, 
the idea is rather suggestive'
All the while the pattern on the screen had never 
changed: the dim network still glowed there challenging 
our sanity. I tried to imagine streets and buildings 
and the creatures going among them, creatures 
would could make their way through the incandescent 
rock as a fish swims through water. It was fantastic ... 
and then I remembered the incredibly narrow range 
of temperatures and pressures under which the human 
race exists. We, not they, were the freaks, for almost
all the matter in the universe is at temperatures of 
thousands or even millions of degrees.
'Well,' I said lamely, 'what do we do now?'
The Professor leaned forward eagerly. 'First we must 
learn a great deal more, and we must keep this an absolute 
secret until we are sure of the facts. Can you 
imagine the panic there would be if this information 
leaked out? Of course, the truth's inevitable sooner or 
later, but we may be able to break it slowly.
'You'll realize that the geological surveying side of 
my work is now utterly unimportant. The first thing 
we have to do is to build a chain of stations to find the 
extent of the structure. I visualize them at ten-mile 
intervals toward the north, but I'd like to build the 
first one somewhere in South London to see how extensive 
the thing is. The whole job will have to be kept 
as secret as the building of the first radar chain in the 
late thirties.
'At the same time, I'm going to push up my transmitter 
power again. I hope to be able to beam the 
output much more narrowly, and so gready increase 
the energy concentration. But this will involve all sorts 
of mechanical difficulties, and I'll need more assistance.'
I promised to do my utmost to get further aid, and 
the Professor hopes that you will soon be able to visit 
his laboratory yourself. In the meantime I am attaching 
a photograph of the vision screen, which although 
not as clear as the original will, I hope, prove beyond 
doubt that our observations are not mistaken.
I am well aware that our grant to the Interplanetary 
Society has brought us dangerously near the total estimate 
for the year, but surely even the crossing of space 
is less important than the immediate investigation of 
this discovery which may have the most profound 
effects on the philosophy and the future of the whole 
human race.

I sat back and looked at Karn. There was much in
the document I had not understood, but the main outlines 
were clear enough.
Yes,' I said, 'this is it! Where's that photograph?' 
He handed it over. The quality was poor, for it had 
been copied many times before reaching us. But the 
pattern was unmistakable and I recognized it at once. 
'They were good scientists,' I said admiringly. 
'That's Callastheon, all right. So we've found the truth 
at last, even if it has taken us three hundred years to do 
it.'
'Is that surprising,' asked Karn, 'when you consider 
the mountain of stuff we've had to translate and the 
difficulty of copying it before it evaporates?'
I sat in silence for a while, thinking of the strange 
race whose relics we were examining. Only once - never 
again - had I gone up the great vent our engineers 
had opened into the Shadow World. It had been 
a frightening and unforgettable experience. The multiple 
layers of my pressure suit had made movement 
very difficult, and despite their insulation I could 
sense the unbelievable cold that was all around me. 
'What a pity it was,´ I mused, 'that our emergence 
destroyed them so completely. They were a clever race, 
and we might have learned a lot from them.'
'I don't think we can be blamed,' said Karn. 'We 
never really believed that anything could exist under 
those awful conditions of near-vacuum, and almost 
absolute zero. It couldn' t be helped.'
I did not agree. 'I think it proves that they were the 
more intelligent race. After all, THEY discovered us first. 
Everyone laughed at my grandfather when he said that 
the radiation he'd detected from the Shadow World 
must be artificial.'
Karn ran one of his tentacles over the manuscript. 
'We've certainly discovered the cause of that radiation,' 
he said. 'Notice the date - it's just a year before 
your grandfather's discovery. The Professor must have 
got his grant all right!' He laughed unpleasantly. 'It 
must have given him a shock when he saw us coming
up to the surface right underneath him.'
I scarcely heard his words, for a most uncomfortable 
feeling had suddenly come over me. I thought of the 
thousands of miles of rock lying below the great city of 
Callastheon, growing hotter and denser all the way to 
the Earth's unknown core. And so I turned to Karn. 
'That isn't very funny,' I said quietly. 'It may be 
our turn next.'


Arthur C. Clarke,  1949

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